[GMcL]

Stem seals can show from a cold start a puff of blue smoke, my SAAB with the GM V6 did that. Using a litre in less than 1,000 miles would usually indicate something more serious.

I had a FIAT Coupë 20v turbo used around a litre of oil every 750-1,000 miles at less than 50,000 miles, no black soot stuck to the rear bumper, no dirty exhaust, it was pistons and rings. A compression test will tell you if things are not as they should be in the cylinders.

My FIAT also started to blow blue smoke after light/no throttle when going back on the throttle at around 90,000 miles, that was a worn turbo.